There are many instances in building construction requiring roofs covering large areas that are not obstructed with intermediate vertical supporting members such as columns. An example is a sporting or events stadium, where unobstructed views can be sold for premium prices. Seats in stadia with obstructed views are sold much more cheaply than those with a clear view. Another example of such a building is an aircraft hangar that must be wide enough and high enough to accommodate an aircraft having a large wing span and a high tail structure. This is especially true with the advent of so called “super-jumbos” such as the Airbus A380.
Various geometric shapes have been proposed in the prior art for roof structures that effectively cover a large area at a relatively low cost and without the use of intermediate supports. For example, it has been proposed that a roof have the shape of a hyperbolic paraboloid. However, such a roof structure may not be suitable as an aircraft hangar as its shape is predominantly ovular and may not be able to cover large aircraft.
Also, various materials are used in the building industry to form roof trusses. For example wood has been used for centuries to form roof trusses, while large modern buildings often employ steel roof trusses to span the width of a building. The I-beam (so called because of the shape of its cross section) also has been used to increase the strength and rigidity of roofs and reduce the weight of a roof structure. To create an I-beam steel webbing can be inserted between two parallel sections of steel. The design increases the torsional strength and moment of inertia of a beam while reducing the weight compared to a solid rectangular beam. Other materials used for beams include composites, alloys and plastics to prevent corrosion caused by chemicals and/or chemical reactions in environments such as phosphate storage facilities and acid storage facilities (e.g., galvanizing plants).
I-beams engineered from wood with fibreboard and a laminated veneer are also becoming increasingly popular in construction, especially residential construction, as such beams are both lighter and less prone to warping than solid wooden beams. However wooden I-beams can suffer a rapid loss of strength in a fire if left unprotected.
Similar to an I-beam, Australian Patent No. 716272 to Berryman discloses roofing beams made of sections that are then bolted or welded together. Each section consists of two parallel rectangular hollow tubes to reduce weight. A metal webbing is welded to the two parallel rectangular hollow tubes in a zig-zag pattern. The result is a lighter, more rigid structure.
However, disadvantages of the Berryman invention include accelerated corrosion rates due to pooling of water on the beam during storage and transportation. Such beams, even when painted or galvanized, once exposed to water when lying flat in a storage position may begin to rust or exfoliate.
The Berryman invention requires a coil of steel to be cut or slit to different widths to accommodate a range of beam sizes, then pressed to form its final shape. This process requires additional specialist equipment to cut the coil. This manufacturing process also requires carrying large stock levels of numerous different beam sizes. Also, due to long beam lengths specialist transportation companies may need to be enlisted to transport the beams.
There is therefore a need for improved beams that increase spanning capability, reduce corrosion, and are relatively easily manufactured and transported.